Technology in reproduction

During the “Cattlemen’s College” sessions at the 2015 Cattle Industry Convention last week, George Seidel, Ph.D., a reproductive physiologist and distinguished professor at Colorado State University’s College of Veterinary Medicine, outlined some present and future technologies in bovine reproduction.

This event marked the 22nd year for the Zoetis-sponsored Cattlemen’s College educational program.

Seidel began with a discussion of sex-sorted semen, a technology he helped develop. Ovulation synchronization and artificial insemination (AI) enable rapid progress in genetic improvement, he says, adding that sex is the most important genetic trait. Adding sexed semen to a synchronization and AI program allows the producer to choose the sex of the offspring, providing a number of opportunities for beef and dairy producers.

However, the process for sorting semen is expensive, not 1000 percent accurate and some fertility is lost, so the technology has limits in terms of practical use. Seidel points out that “male” or “female” sperm cells, those carrying either Y or X chromosomes, are essentially identical in size, shape and electrical charge. Those with X chromosomes, however, contain about 4 percent more DNA than those with Y chromosomes. A sophisticated and expensive (about $500,000) machine using lasers, dies and high-voltage deflection plates exploits that small difference to sort the sperm cells with 90 to 95 percent accuracy.

Because of the time and expense involved, sexed semen generally costs about $20 more per dose than conventional semen, and fertility is somewhat reduced. Seidel says data from Select Sires on 25,000 services show first-service pregnancy rates ranging from 45 to 56 percent using sexed semen.

Sexed semen has a variety of potential applications. In beef herds, Seidel says, producers could choose to use sexed semen to breed heifers to produce heifer calves. This could result in fewer cases of dystocia, while also accelerating genetic progress. If a rancher is selecting for genetic improvement, the replacement heifers should be the best females in the herd, so breeding them with sexed semen from superior sires will foster further improvement in the next generation of replacement heifers.

Dairies commonly use sexed semen to produce replacement heifers from their best, most productive cows, and use conventional semen with the rest of the herd.